Medical imaging utilizes scintillators for translating gamma rays or x-rays into optical photons. The scintillators are commonly coupled to photodetectors such that the resultant optical photons can be translated into electric current. In this fashion gamma-rays and x-rays may be detected and utilized in applications such as positron emission tomography (PET), computed tomography (CT), single photon emission computed tomography (SPECT), and x-ray imaging. In these applications, the location of the interaction of the gamma ray or x-ray is determined by the response of the photodetector to the optical photons.
The characteristics and performance of the scintillator, therefore can play a significant role in the imaging performance. The scintillator thickness, for example, must often be increased in order to stop the incoming gamma rays or x-rays with the required efficiency. As the thickness increases, however, the spreading of emitted optical photons within can degrade the spatial resolution of the detector. In order to preserve the spatial information contained in the optical photons, it is desirable to have a scintillator that is optically anisotropic so that the emitted photons are preferentially transported to the photodetector near the point in the scintillator where the gamma ray or x-ray interacted with the scintillator. In applications that rely on centroid detection to determine the position of the interaction, precise control of the optical anisoptropy is needed to preserve the spatial information. In addition, precise control is need to allow enough spreading of the signal such that it is shared amongst discrete detector element in such a way as to allow reliable centroid determination. Thus an improved method of controlling the spreading of optical photons within a scintillator would be highly desirable.
Existing approaches to this control have addressed the problem by assembling scintillator packs or blocks from discrete elements, often separated by reflectors. Other approaches generate discrete elements by growing scintillator crystals with a fine needle-like structure. Assembling the scintillator blocks from these discrete elements, however, can be extremely time consuming, and relying on the growth of the needle-like scintillator crystals often does not allow for the precise control over optical properties using existing methods.
In the case of PET scintillator blocks, a wide variety of surface treatments and reflector elements have been used to control the sharing of light between the discrete elements of the block. These treatments and applications further complicate construction. Another method has been to use a saw to make deep grooves into the scintillator in a grid pattern to provide optical isolation between different regions of the scintillator. Often such isolation is only partial. The saw cuts are often filled with a reflective material to improve the optical properties. This saw cut method has the disadvantage of generating relative large dead areas by removal of the scintillator material.
It would, therefore, be highly desirable to have a method of manufacturing an anisotropic scintillator that provided precise control of optical photon spreading within the resultant scintillator. It would additionally be highly desirable to have a method of manufacturing an anisotropic scintillator that was cost effective, reliable, and did not generate unwanted dead space.